Field of the Invention
The present invention relates to an idle control system for an internal combustion engine used to drive an electric generator.
Motor generator sets comprising an AC generator and an internal combustion drive engine are widely used. In general, idle control systems for controlling the speed of the drive engine are known. A speed responsive governor is utilized to maintain a relatively constant engine speed regardless of load, except during periods when there is no load on the generator. An idle control circuit detects the absence of a load on the generator and actuates an electronic device, such as a solenoid or an electromagnet, cooperating with the engine throttle to decrease the speed of the engine to a predetermined idle speed. Examples of such systems are described in U.S. Pat. Nos. 3,612,892 issued to Nobile et al on Oct. 12, 1971 and 3,626,197 issued to Zanzarella et al on Dec. 7, 1971, both commonly assigned with the present invention. The disclosures of such patents are herein incorporated by reference.
Such prior art idle control circuits, however, are disadvantageous in that they are relatively expensive both in terms of component costs, and power dissipation. In particular, the prior art idle circuits tend to dissipate power even when the electromagnet is not activated. An electronic switching device is used to short out the electromagnet coil when a current draw from the generator is sensed. The electromagnet is connected in series with a diode and a high power resistor (utilized to limit the current when the electromagnet coil is removed from the circuit). When the electronic switching device is rendered conductive, the current continues to flow through the current limiting resistor. Accordingly, the prior art circuits tend to dissipate on the order of 25 watts of power, and require appropriate provisions for heat removal.
Further, prior art systems for use with AC generators, such as described in the Nobile et al U.S. Pat. No. 3,612,892, utilize a current transformer having a primary winding interjected into the output line of the generator. Current drawn from the generator causes generation of a current in the secondary coil of the transformer, which is utilized to render the switching device conductive and short out the coil of the electromagnet. The primary coil of the transformer, however, requires a plurality of turns of relatively heavy (high gauge) magnet wire. The high gauge of the wire and requirement of a plurality of turns necessitates that the transformer be hand wound, and typically be connected to the other circuitry by hand.